1. Field of the Invention
The present invention relates to a circumferential flow pump that is housed in the fuel tank of an automobile, for example, and that supplies fuel to the internal combustion engine at a prescribed pressure.
2. Description of the Related Art
Circumferential flow pumps are known that employ the following measures to increase the pump output power with the same outside dimensions and under the same operation conditions (e.g., Japanese Patent No. 2,962,828). The centers of the radii of annular feed passages are set approximately coincident with the centers of the radii of an impeller, respectively, and the former radii are set equal to the latter radii, respectively. Further, the centers of the above radii are located inside the outline of the impeller. These measures are effective in increasing the C factor of circulating flows (Qc) and thereby increasing the efficiency.
High pump performance is attained by the following measures (e.g., JP-A-6-2690). The impeller is made of a synthetic resin. An impeller plate is formed with a side surface of one impeller groove that communicates with one end surface and an outer circumferential surface of the impeller, a side surface of the other impeller groove that communicates with the other end surface and the outer circumferential surface of the impeller, and a side surface of a communication groove that communicates with the one impeller groove and the other impeller groove in the axial direction on the outer circumference side. The communication groove is located between the one impeller groove and the other impeller groove and is terminated at a position that is inside the outer circumference of the impeller plate. A partition wall is formed so that the interval between the bottom surface of the one impeller groove and the bottom surface of the other impeller groove gradually decreases toward the outer circumference and has a prescribed value or more at the most outer circumference where the bottom surfaces are terminated.
In the above-described conventional circumferential flow pumps, the centers of the radii of the annular feed passages are set approximately coincident with the centers of the radii of the impeller, respectively, and the centers of the radii are located inside the outline of the impeller. In these circumferential flow pumps, as described in JP-A-6-2690, an inactive portion occurs between two symmetrical swirling flows in the impeller grooves. In the inactive portion, liquid fuel is not given a sufficiently high flow velocity and a backward flow occurs. The backward flow prevents fuel pressure increase; even if the C factor of circulating flows (Qc) is increased to produce a high pressure, the internal pressure leakage makes it difficult to increase the fuel pressure. The influence of this pressure leakage is small in the case of an ordinary pump operation. However, for example, when the voltage applied to an electric motor for giving drive force to the circumferential flow pump is low, the pressure leakage is so serious as to make it difficult to obtain a high pressure.